Bundle branch reentrant ventricular tachycardia

INTRODUCTION — Bundle branch reentrant ventricular tachycardia (BBRVT) is a unique arrhythmia because the tachycardia circuit is dependent exclusively on the specialized conduction system. This has two important implications: a large portion of the circuit can be recorded directly, and the circuit is uniquely sensitive to the effects of focal ablation. The circuit involves antegrade conduction over the right bundle branch and retrograde conduction over the left bundle branch; the His bundle is adjacent to but separate from the circuit.

BBRVT can be very rapid (often >200 beats per minute), often resulting in syncope or cardiac arrest. It is a relatively rare arrhythmia, usually seen in patients with advanced structural heart disease, and it forms part of the differential diagnosis of wide complex tachycardias (in addition to myocardial VT, supraventricular tachycardia [SVT] with aberrancy of the left bundle branch, and pre-excited tachycardias using nodofascicular or atrial fascicular bypass tracts). (See "Wide QRS complex tachycardias: Approach to the diagnosis".)

A related disorder, intrafascicular reentry (also called idiopathic left ventricular tachycardia), utilizes the separate fascicles of the left bundle branch. It, too, is typically observed in patients with advanced structural heart disease but may also be seen in patients with structurally normal hearts [1,2]. Both arrhythmias depend on conduction delay in the His-Purkinje system. (See "Ventricular tachycardia in the absence of apparent structural heart disease", section on 'Idiopathic left ventricular tachycardia'.)

The mechanisms, clinical features, diagnosis, and treatment of BBRVT will be discussed here. The general approach to wide QRS complex tachycardias as well as the treatment of VT of other etiologies (ie, ischemic, scar-related) are discussed separately. (See "Wide QRS complex tachycardias: Approach to the diagnosis" and "Sustained monomorphic ventricular tachycardia in patients with structural heart disease: Treatment and prognosis".)

EPIDEMIOLOGY — The exact incidence of BBRVT has been difficult to quantify, given that the diagnosis is typically only confirmed following invasive electrophysiology studies. Several small series have reported incidences ranging from as low as 3 to as high as 20 percent, but most series are likely subject to referral bias, making the true incidence of BBRVT in the general population difficult to define [3-6].

MECHANISM AND THE RESULTANT ELECTROCARDIOGRAM (ECG) — With BBRVT, the arrhythmia begins when one or more premature ventricular beats arise and conduct into both the right bundle branch, where retrograde activation is blocked due to refractoriness from the preceding normally conducted antegrade beat, and into the left bundle branch, which has a shorter refractory period than the right bundle branch (figure 1). As a result, the impulse conducts retrogradely up the left bundle branch to the bundle of His, although the His bundle is not an essential component of the circuit. The impulse then conducts antegradely down the right bundle branch, activating the ventricle at the termination of the right bundle branch. For this reason, the QRS during VT has a left bundle branch block (LBBB) pattern and may closely resemble the sinus rhythm QRS if baseline LBBB is present. If the timing is right and slow conduction through the circuit allows for recovery from refractoriness of all of the component parts, sustained reentry may be established.

It is important to consider that although we speak of LBBB as an electrocardiographic pattern, the phenomena is typically a delay rather than a block, as retrograde complete LBBB would make this arrhythmia circuit impossible.

CLINICAL FEATURES — BBRVT, usually seen in patients with advanced structural heart disease, occurs with both ischemic and nonischemic heart disease [3,7,8]. The heart disease is usually severe with cardiomegaly and a history of heart failure (HF); however, BBRVT may occur in the absence of structural heart disease in the setting of isolated conduction disturbances in the His-Purkinje system [9].

Symptoms — Patients with BBRVT may variably experience palpitations. In most instances, patients will present with presyncope, syncope, or sudden cardiac arrest (SCA). Because BBRVT rates are typically rapid (>200 beats per minute) and because BBRVT most commonly occurs in patients with advanced structural heart disease, hemodynamic instability leading to syncope or SCA is common.

ECG findings — When VT develops, antegrade conduction down the right bundle branch with delayed depolarization of the left ventricle results in a VT with a typical left bundle branch block (LBBB) appearance (waveform 1). In some patients, however, the reverse sequence of conduction occurs, leading to a right bundle branch block (RBBB) appearance. The PR interval may be normal or prolonged. The mean electrical axis is usually about +30º, but a conduction defect in the left anterior fascicle will produce a marked leftward (superior) axis deviation (figure 2).

In sinus rhythm, most patients with BBRVT have a prolonged QRS (nonspecific conduction delay or LBBB), and most have a prolonged His-to-ventricle (HV) interval. Most patients have a similar ECG during sinus rhythm because of the underlying prolongation of the HV interval (waveform 1). A prolonged HV interval has been put forth as a prerequisite for developing sustained reentry within the bundle branches [3,10-13]. However, HV prolongation in sinus rhythm is not present in all cases, suggesting that BBRVT can result from functional conduction abnormalities in the His-Purkinje system [14].

EPS findings — During invasive electrophysiology study (EPS), the most important recording is the His bundle recording during induced VT. During BBRVT, the HV is typically similar to, or a little longer than, the HV that is recorded in sinus rhythm. During other forms of VT, the HV is usually negative (ie, shorter than sinus rhythm). In addition, if there are irregularities in the cycle length, changes in the His-to-His interval precede changes in the V-to-V interval.

DIFFERENTIAL DIAGNOSIS — The differential diagnosis of BBRVT includes all of the usual causes of wide QRS complex tachycardia, including:

●VT of other types (monomorphic, polymorphic)

●SVT with aberrant conduction

●SVT with pre-excitation

●SVT with ventricular pacing

●Artifact mimicking wide QRS complex tachycardia

BBRVT has a rather "typical" left bundle branch block (LBBB) pattern as does an SVT with pre-existing or functional BBB. In comparison, an "atypical" LBBB pattern (slurring of the initial QRS forces) favors myocardial VT or pre-excited tachycardia. While the presence of BBRVT may be suspected from the surface ECG, definitively establishing the diagnosis often requires electrophysiologic testing to differentiate this arrhythmia from other forms of VT. The general approach to wide complex tachycardias is discussed separately. (See "Wide QRS complex tachycardias: Causes, epidemiology, and clinical manifestations", section on 'Differential diagnosis of WCT' and "Wide QRS complex tachycardias: Approach to the diagnosis".)

DIAGNOSIS — The diagnosis of BBRVT is suggested from the surface ECG recorded during VT. BBRVT is suggested on the surface ECG by the following characteristics:

●Left bundle branch block (LBBB) morphology (although so-called "reverse" BBRVT may also occur, with activation of the ventricles over the left bundle branch, producing a right bundle branch block [RBBB] QRS morphology)

●The His-to-ventricle (HV) interval during VT is typically longer than during sinus rhythm

●During spontaneous changes in cycle length, changes in the H-H interval precede and predict changes in the V-V interval

Typically, however, confirmation of the diagnosis is made during invasive electrophysiology studies (EPS). During BBRVT, the HV is typically similar to, or a little longer than, the HV that is recorded in sinus rhythm, in contrast to the HV findings in other forms of VT.

TREATMENT — Treatment is frequently necessary in BBRVT, since BBRVT typically occurs in the presence of significant heart disease and often leads to hemodynamic compromise that can result in presyncope, syncope, or SCA. Radiofrequency catheter ablation is curative in most patients, although some patients may also be candidates for an implantable cardioverter-defibrillator (ICD) for secondary or primary prevention based on the presence of other structural heart disease. Antiarrhythmic drug therapy is rarely used given the high risk of BBRVT recurrence.

Catheter ablation — For patients with symptomatic BBRVT, we recommend treatment with radiofrequency catheter ablation, rather than antiarrhythmic drug therapy or ICD implantation alone. This approach is based on the high efficacy of catheter ablation for curing BBRVT, the significant hemodynamic compromise which results from BBRVT in most patients, and the relatively poor efficacy of antiarrhythmic drug therapy in treating this arrhythmia. This approach is consistent with the guidance provided by multiple professional society guidelines [15]. The 2019 HRS/EHRA/APHRS/LAHRS Expert Consensus Statement on Catheter Ablation of Ventricular Arrhythmias recommended catheter ablation for reducing the risk of recurrent BBRVT [16,17]. Reentrant fascicular tachycardia has also been treated successfully using ablation [1,2].

Because the circuit of BBRVT is so well defined and because the main circuit components (right bundle branch, left bundle branch) are easy to locate, catheter ablation for BBRVT is conceptually and mechanically simple. Most commonly, catheter ablation of the right bundle branch is performed, leading to complete right bundle branch block (RBBB). In this procedure, a catheter is inserted into the femoral vein and passed through the tricuspid valve until a right bundle electrogram is recorded. Ablation at this site typically leads to nearly immediate production of RBBB, which predicts the absence of recurrent VT (waveform 1 and waveform 2 and waveform 3).

BBRVT has also been treated by ablation of the left bundle [18,19]. This provides the theoretical advantage of preventing the need for pacing, as the relatively normal right bundle branch remains unaffected. It is not so often performed, however, since this procedure requires arterial access and localization of the left bundle is more difficult than the right bundle. In addition, the majority of patients with BBRVT require ICD therapy anyway. (See 'ICD therapy' below.)

Multiple small observational studies have demonstrated nearly universal success of catheter ablation [2,4,8,10,11,19-23]. The largest observational series described a cohort of 32 patients (treated between 2005 and 2016) who had successful ablation of the right or left bundle branch at a single center. The procedure was well tolerated, with only one patient developing complete heart block; over a mean follow-up of almost eight years, no patient had recurrent BBRVT [24]. The efficacy and safety of catheter ablation is also supported by indirect evidence and more extensive experience in other settings, including for both ventricular and supraventricular arrhythmias. (See "Overview of catheter ablation of cardiac arrhythmias" and "Sustained monomorphic ventricular tachycardia in patients with structural heart disease: Treatment and prognosis", section on 'Radiofrequency catheter ablation' and "Atrioventricular nodal reentrant tachycardia", section on 'Catheter ablation' and "Treatment of arrhythmias associated with the Wolff-Parkinson-White syndrome", section on 'Catheter ablation'.)

Antiarrhythmic drug therapy — BBRVT is often resistant to antiarrhythmic drug therapy [10,11]. In a study of catheter ablation for BBRVT in the 1990s, seven patients were treated successfully with catheter ablation after failure of a mean of 3±1 antiarrhythmic drugs [10]. In a different non-randomized study from the 1990s comparing the efficacy of catheter ablation and antiarrhythmic drugs, ablation successfully eliminated the arrhythmia in all patients, while only 62 percent of patients treated with antiarrhythmic drugs had no recurrent VT [11]. As such, we limit use of antiarrhythmic drugs for the treatment of BBRVT to two subsets of patients:

●Patients who are not a candidate for, or refuse, catheter ablation

●Patients with recurrent symptomatic VT following catheter ablation in whom antiarrhythmic drug therapy is administered to reduce the likelihood of recurrent ICD shocks.

ICD therapy — Following catheter ablation for BBRVT, repeat electrophysiologic studies generally reveal an inability to induce BBRVT. However, VT of myocardial origin can be induced in some cases, although only a small number of patients have been studied. Because of the concurrent underlying structural heart disease, outcomes are often quite poor in patients followed after successful ablation of BBRVT. Sudden cardiac death (SCD) has been reported, and progressive HF is frequent [23,25]. Due to the severity of underlying cardiac disease, many patients are candidates for ICD therapy for the primary or secondary prevention of SCD following catheter ablation for BBRVT [15]. (See "Secondary prevention of sudden cardiac death in heart failure and cardiomyopathy", section on 'Summary and recommendations' and "Primary prevention of sudden cardiac death in patients with cardiomyopathy and heart failure with reduced LVEF".)

SOCIETY GUIDELINE LINKS — Links to society and government-sponsored guidelines from selected countries and regions around the world are provided separately. (See "Society guideline links: Ventricular arrhythmias".)

INFORMATION FOR PATIENTS — UpToDate offers two types of patient education materials, "The Basics" and "Beyond the Basics." The Basics patient education pieces are written in plain language, at the 5^th to 6^th grade reading level, and they answer the four or five key questions a patient might have about a given condition. These articles are best for patients who want a general overview and who prefer short, easy-to-read materials. Beyond the Basics patient education pieces are longer, more sophisticated, and more detailed. These articles are written at the 10^th to 12^th grade reading level and are best for patients who want in-depth information and are comfortable with some medical jargon.

Here are the patient education articles that are relevant to this topic. We encourage you to print or e-mail these topics to your patients. (You can also locate patient education articles on a variety of subjects by searching on "patient info" and the keyword(s) of interest.)

●Basics topics (see "Patient education: Ventricular tachycardia (The Basics)")

SUMMARY AND RECOMMENDATIONS

●Bundle branch reentrant ventricular tachycardia (BBRVT) is a unique arrhythmia because the tachycardia circuit is dependent exclusively on the specialized conduction system. The circuit most commonly involves antegrade conduction over the right bundle branch and retrograde conduction over the left bundle branch; the His bundle is adjacent to but separate from the circuit. (See 'Introduction' above.)

●Patients with BBRVT typically have advanced structural heart disease, either ischemic or nonischemic heart disease. Presyncope, syncope, or sudden cardiac arrest are the common presenting symptoms of BBRVT. (See 'Clinical features' above.)

●The diagnosis of BBRVT is suggested from the surface electrocardiogram (ECG), on which BBRVT has a rather "typical" left bundle branch block pattern. While the presence of BBRVT may be suspected from the surface ECG, definitively establishing the diagnosis often requires electrophysiologic testing to differentiate this arrhythmia from other forms of VT. (See 'ECG findings' above and 'Diagnosis' above.)

●For patients with symptomatic BBRVT, we recommend treatment with radiofrequency catheter ablation, rather than antiarrhythmic drug therapy or implantable cardioverter defibrillator (ICD) implantation alone (Grade 1B). This approach is based on the high efficacy of catheter ablation for curing BBRVT, the significant hemodynamic compromise which results from BBRVT in most patients, general safety and tolerability of catheter ablation, and the relatively poor efficacy and greater side effects of antiarrhythmic drug therapy in treating this arrhythmia. (See 'Treatment' above.)

●Depending on the severity of concurrent underlying structural heart disease in patients with BBRVT, many patients are candidates for ICD therapy for the primary or secondary prevention of sudden cardiac death following catheter ablation for BBRVT. (See 'ICD therapy' above.)